fix: split components under preserved root resetting the preserve

[mlrawlings]

Description

Split components did not have the parent's preserved value attached to them, but in endComponent we're setting the current ___isPreserved back to the parent's value regardless of whether the current component was split.

This caused a split component to set the ___isPreserved back to undefined, which meant any components after this would not be hydrated.

This fixes the issue by ensuring all components that render boundaries have their parent's ___isPreserved value.

Checklist:

• I have read the CONTRIBUTING document and have signed (or will sign) the CLA.
• I have updated/added documentation affected by my changes.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Merging #1559 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1559   +/-   ##
=======================================
  Coverage   90.54%   90.54%           
=======================================
  Files         355      355           
  Lines       12764    12764           
=======================================
  Hits        11557    11557           
  Misses       1207     1207           

Impacted Files	Coverage Δ
...ges/marko/src/runtime/components/beginComponent.js	100.00% <100.00%> (ø)

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